1. Field of the Invention
The present invention relates to the field of power electronics. It relates specifically to a high-power semiconductor module as claimed in the preamble of patent claim 1.
2. Discussion of Background
In present-day converters having very little stray inductance and no protection circuit, all the energy of an energy-storage capacitor discharges in a few microseconds in the event of a short circuit. In the process, currents in the region of several hundred kilo amperes and power levels in the region of 100 MW occur. A short circuit therefor often leads to an explosion, in which fragments of the semiconductor element and of the casing are projected outward like projectiles.
In the planning of modules, it is therefore necessary to consider the following aspects for an explosion situation: firstly, nobody must be injured. This is achieved by accommodating the modules in an area which must not be entered during operation.
Secondly, consequential damage to objects, in particular to adjacent modules and busbars, should be prevented. In general, this requirement is virtually impossible to achieve satisfactorily.
DE-A-30'32'133 discloses a high-power semiconductor module having a semiconductor element, two electrodes between which the semiconductor element is clamped, and an insulating casing which encloses the semiconductor element. This module has an explosion protection element in the form of a single-piece or multi-piece hollow cylinder composed of a soft, elastic silicone rubber, which is inserted into the insulating casing (which is manufactured from ceramic) such that it encloses the semiconductor element. Molten metal which is projected outward in the event of an explosion is intended to be trapped by the explosion protection element and its kinetic energy is intended to be absorbed as far as possible, in order to protect the ceramic casing and other adjacent elements of the module against being struck by hot metal. In order to ensure this, the explosion protection element must have a high capability to absorb kinetic energy and, furthermore, must be heat-resistant in order that it is not melted by the explosion itself.
A disadvantage of such a design appears to be that the original module is enlarged by the space required for the protection element. Furthermore, it cannot be used in combination with any desired casing shapes. In addition, the kinetic energy cannot be completely absorbed in all cases, so that shocks are transmitted through the protection element to the insulating casing. If the semiconductor module has a ceramic casing as is disclosed in this document, then the natural robustness of the insulating casing may be sufficient for explosion protection. However, if the insulating casing is manufactured from plastic, then residual energy levels can quite possibly lead to destruction of the insulating casing, and to the formation of new ejected projectiles.
DE-C-26'61'120 likewise discloses an explosion protection element, which, however, is arranged outside a module casing. The explosion protection element surrounds the casing with a gap in the radial direction, by which means a cavity is formed, which is intended to be used to reduce the pressure in the event of an explosion. To do this, the cavity must be considerably larger than the area enclosed by the casing. A disadvantage of this design is, once again, the increased space required.